1. Field
The embodiments discussed herein are directed to a solid state image sensing device, for example a CMOS image sensor, on which a plurality of pixels are disposed in a matrix, which may relate to a solid state image sensing device using a shared type pixel in which a part of a transistor or the like for pixel data read is shared by a plurality of pixels.
2. Description of Related Art
A video camera or a digital camera uses a CCD or CMOS solid state image sensing device. In such a solid state image sensing device, a plurality of pixels each having, for example, a photo diode are disposed in a matrix as a light receiving unit and an incident light into each pixel is converted to electron by the photo diode to generate charge signal. The generated charge signal is outputted to the outside via a signal line.
FIG. 1 shows a pixel disposed in such a matrix and a prior art read circuit for reading the data of the pixel. FIG. 1 shows an example of the CMOS image sensor, which is an active photo sensor (APS) comprises a photo diode corresponding to the pixel and four transistors for pixel data read.
In FIG. 1 light received by a photo diode (PD) 101 is converted to electron and transferred to a floating diffusion layer (FD) by a transfer gate transistor (TG-Tr) 102. The FD converts charge signal transferred from PD 101 to a voltage. The voltage is inputted to a source follower transistor (SF-Tr) 103 and a drive capability is amplified. Then, the voltage is outputted to the outside via a select transistor (SL-Tr) 104 for selecting a row. A voltage of the FD can be reset by a reset transistor (RS-Tr) 105.
As shown in FIG. 1, in an APS, which comprised four transistors for data read that are provided for a photo diode, a shared type pixel, in which at least a part of a transistor or the like for data read is shared by a plurality of pixel for the purposes of miniaturization of device, scaling down and a low cost, is became to used. FIG. 2 shows a prior art transistor sharing method in such a shared type pixel. In FIG. 2 although a transfer gate transistor TG-Tr is provided for each of four photo diodes (PD1˜PD4), respectively, the other three transistors of a reset transistor, a source follower transistor and a select transistor are shared.
Such shared type pixel as shown in FIG. 2 is formed, for example, by disposing a photo diode layer and transistors on a silicon substrate, in such a shared type pixel is it difficult to dispose them on the substrate at perfectly equal intervals (center pitch) between pixels, especially photo diodes as a light receiving unit compared with the case where all the transistors for data read are provided for each pixel. Although the circuit shown in FIG. 2 corresponds to FIG. 4 of Patent Document 1 as the prior art of a solid state image sensing device, in FIG. 4 too it is clear that intervals between light receiving areas are not perfectly the same, intervals between at least some light receiving areas are shorter.
In order to improve a light receiving efficiency of a light receiving device corresponding to each pixel in an image sensor, generally an on-chip micro-lens (hereinafter omitted as “micro-lens”) is provided on the surface of a photo diode. Generally all the intervals (center pitches) between micro-lenses are the same like the case where all of the transistor for data read are provided for each pixel.
In the case when all the intervals between micro-lenses are the same, and intervals between light receiving devices, for example photo diodes corresponding to pixels are not the same, there is a problem that a light receiving sensitivity differs by pixels in which, for example a deviation occurs between the center position of the light receiving area of the photo diode and the center position of the micro-lens.
For example, if three transistors are disposed between the disposition area of PD2 and that of PD3 as in the circuit shown in FIG. 2, there is a problem in which periodic stripes occur on the screen due to the difference in sensitivity between pixels since these three disposition areas are connected in a traverse direction, i.e., a horizontal direction.
Patent Document 2 as the prior art of such a solid state image sensing device and the like discloses a technology for reducing the amount of shading by deviating the center positions of a micro-lens and a color filter away from the center position of a light receiving unit in the circumference of the screen in order to prevent color shading caused by the oblique direction of an incident light in the circumference of the screen, specifically the color imbalance of RGB between the center and the circumference in a solid state image sensing device provided with a color filter between the micro-lens and the light receiving unit.
The similar Patent Document 3 discloses the forming method of a micro-lens in which there is design constraint and less forming difficulty and in which the amount of light received by a light receiving device in the circumference can be effectively prevented from decreasing.
However, the problem that the center position of the photo diode as a light receiving unit deviates away from that of the micro-lens the intervals between which are almost perfectly uniform in an image sensor using a shared type pixel in which the intervals between micro-lenses are not perfectly uniform and quality as the output of the image sensor deteriorates cannot be solved.    Patent Document 1: Japanese Patent Application Publication No. 2001-298177, “Solid State Image Sensing Device and Image Sensing System”    Patent Document 2: Japanese Patent Application Publication No. 2001-160973, “Solid State Image Sensing Device and Electronic Camera”    Patent Document 3: Japanese Patent Application Publication No. 2004-296590, “Micro-lens Forming Method in Image Sensing Device”